1. Field of the Invention
The present invention relates to a wavelength conversion member, a backlight unit, a liquid crystal display device, and a method of manufacturing a wavelength conversion member.
2. Description of the Related Art
A flat panel display such as a liquid crystal display device (hereinafter also referred to as “LCD”) has been more widely used as a space-saving image display device having low power consumption. A liquid crystal display device includes at least a backlight unit and a liquid crystal cell and typically further includes a member such as a backlight-side polarizing plate or a visible-side polarizing plate.
In the flat panel display market, the improvement of color reproducibility has progressed in order to improve the performance of a LCD. Regarding this point, recently, quantum dots (also referred to as QDs) have attracted attention as a light emitting material (refer to US2012/0113672A). For example, in a case where excitation light emitted from a backlight is incident on a wavelength conversion member including quantum dots, the quantum dots are excited to emit fluorescence. Here, by using quantum dots having different light emitting properties to emit various kinds of bright light including red light, green light, and blue light, white light can be realized. Since fluorescence emitted from quantum dots has a small full width at half maximum, the obtained white light has not only high brightness but also excellent color reproducibility. Due to the progress of such a three-wavelength light source technique using quantum dots, the color reproduction range has been widened from 72% to 100% in terms of the current TV standard (full high definition (FHD), National Television System Committee (NTSC)) ratio.
In general, in order to improve the durability of quantum dots, the quantum dots are mixed with a ligand material such that peripheries of the quantum dots are coated with the ligand material. For example, JP2013-544018A discloses a method including: mixing quantum dots with amino polystyrene or polyethyleneimine; curing the mixture; crushing the cured product into clusters; and dispersing the clusters in a polymer material. In addition, JP2013-544018A also discloses a phosphor material which is formed of an amino silicone-epoxy emulsion in which amino silicone is used as a ligand material to be mixed with quantum dots.
According to JP2013-544018A, by imparting light scattering properties to a wavelength conversion member, the optical path length of primary light incident on the wavelength conversion member can be increased, and the use efficiency of the primary light can be improved. Further, JP2013-544018A discloses that the efficiency of a backlight unit into which the wavelength conversion member is incorporated is improved. The clusters described in JP2013-544018A have light scattering properties. Therefore, the wavelength conversion member including the clusters can improve the use efficiency of primary light.